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362                  '        METALLURGY OE IRON AND STEEL*
XVII-J! Mil be of- inter;est 'as giving the results of an iuvestigation by Hadfield.? After-making allowances for variations in other ele-t merits, it will" be found-that aluminum has little effect upon the tensile strength, while it _ does not materially injure-the ductility until a content of £ per cent, is reached.
' These conclusions do not agree with the results which I have found1 by casting different alloys in 6-inch square ingots. The aluminum was added in a solid state and possibly was not dissemi^ nated uniformly, but the analysis ,was made on the test-bar itself* and the fusible nature of the. metal, makes it, probable that the piece would be• reasonably homogeneous. Either two. or three ingots were; cast from each heat, the .first containing either no aluminum oft only a trace, while the others were made so as to give fairly rich alloys. The'results are given in Table XYII-K.
The casting and working of such ingots is a regular operation at the works where'these experiments were made, and perfect uniformity is always obtained in respect to tensile strength, so that it-is probable the variations in. bars of the same heat -are due. to the ••• different contents of aluminum. These changes are as! follows: '. •:'.-.:              '.-.:•''                            •
.(1) .The addition of one-half of 1 per cent, of aluminum increases the tensile strength between 3000 and 8000 pounds per square inch, exalts the elastic limit in abo.ut the same proportion, and injures very materially tije, elongation and contraction of area. The effect both upon strength and ductility is more marked in the case of low than in high steels.
(#) The addition of another half of 1 per cent, does not have much effect upon the ultimate strength or the elastic limit, but it still further; decreases the ductility of the metal.
It is stated:bylOdelstjernat that the use of aluminum, irt the manufacture of steel castings, giVes an inferior metal, even though the addition amount to only ,002 per cent., and that such ;steel presents a peculiar fracture, the faces of the crystals being large and well defined. It must be kept in mind, however, that these conclusions 'apply to one,particular kind of practice, and that the use of aluminum, under certain, conditions, ;may produce a most — j- i           ^,           . .,              . ,: . ___
* Aluminum Steel.   JoutrfttlI. and, 8,1., Voi II, 1890, p. 161.
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